A form device for cellular concrete, including a number of piled-up form units having a heat-insulating bottom and shell, a heat-insulating top board, and a bottom-to-shell joint. A cellular concrete manufacture is produced by mixing cement with warm water at a temperature of 40.degree. to 75.degree. C. to form a warm cement mortar, mixing the mortar with a bubbled warm frother solution to form a warm cellular concrete paste, and hardening the paste using such heat-insulating form device.